This invention relates to a vehicular navigation apparatus which provides guidance along a path by outputting guidance information for travel to a desired destination.
A navigation apparatus for automotive vehicles is adapted to provide course guidance for travel to a desired destination to a driver who is unfamiliar with the local geography. Recent years have seen extensive development of such navigation apparatus.
Conventionally, a vehicular navigation apparatus relies upon so-called "route matching" in which a course is set from a starting point to a desired destination before the vehicle begins travelling, with course guidance being provided to the driver in accordance with the course set. In some of these apparatus, a map is displayed on the screen of a CRT and the course is superimposed on the map if the driver designates a specific course. In a case where the navigation apparatus designates an intersection at which a turn is to be made next in accordance with the preset course, the distance to this intersection is displayed numerically or in the form of a graph. When a turn is to be made at an intersection using such a navigation apparatus, the driver observes the course displayed on the map to decide the next intersection at which the turn is to be made, or the driver looks at the numeric or graph display to ascertain the distance to the intersection where the turn is to be made, thereby determining the proper intersection.
However, as mentioned above, the conventional navigation apparatus is such that a course is set from a starting point to a desired destination before the vehicle begins travelling and course guidance is provided to the driver in accordance with the course set. Consequently, if the driver should happen to mistake an intersection and depart from the set course, travel in accordance with the guidance provided by the navigation apparats will not be able to continue unless the vehicle is returned to the set course. In addition, a decision as to whether or not a predetermined intersection has been passed as specified by the course guidance is based upon detection of travelled distance or a left or right turn as detected by a distance sensor or steering angle sensor, respectively. In actuality, however, detection of travelled distance and steering angle is susceptible to considerable error, which can cause the navigation apparatus to make errors in judgment.
Accordingly, an apparatus for guiding a driver to a route leading to a desired destination even when the driver has strayed off a set course has been proposed in Japanese Patent Application Laid-Open (KOKAI) No. 61-21610.
This proposed navigation apparatus comprises means for detecting that a vehicle has strayed from a course of planned travel, means for detecting an intersection on a course of planned travel that is for the purpose of returning the vehicle from its present position, means for detecting the direction to the return intersection with respect to the forward direction of the vehicle, and means for displaying guidance information necessary for guiding the vehicle along the course of planned travel as well as information indicating the direction to the return intersection with respect to the forward direction of the vehicle.
With the apparatus disclosed in the abovementioned application, however, a course is set at the moment a departure (starting) point and desired destination are entered, and guidance is provided on the assumption that the vehicle will travel along this course. Consequently, if the vehicle strays from the course, it becomes necessary to return the vehicle to the course and the present position of the vehicle must be reset. As a result, difficulties are encountered in dealing with occasions where the vehicle departs from a course and in coping with the will of the driver.
The applicant has filed a patent application (U.S. Ser. No. 07/260,213, filed Oct. 20, 1988) proposing a novel navigation apparatus which relies upon an explorer system instead of the above-described route matching system. In accordance with this system, the coordinates of a plurality of geographical points (e.g., intersections, characterizing structures, etc.) are set and a desired destination is entered, whereupon a course is sought from each geographical point to the desired destination and outputted as guidance information. Navigation is possible even if distance, steering angle and geomagnetic sensors should happen to fail or even if these sensors are not provided. As a result, if the driver strays from a course or changes the desired destination, the apparatus readily provides the driver with guidance to the destination. However, a system through which desired destination, present position and the like can be inputted in simple fashion is required for this navigation apparatus.